COSC 1P03

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Cosc 1P03
Example is not the main thing in influencing
others, it is the only thing. Albert
Schweitzer
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Arrays

• collections of values (objects)
• elements
• use
• declare
• create
• process
• memory model
• length attribute
• Returns the size of the array.
• RainFall Example
• Print out only those months with above average
  rainfall.
• Palindrome Example
• Strings as array of char
• toCharArray String(char)

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RainFall

• private void display ( )
• String year // year
• double rainfall // rainfall for each
  month
• double totRain // total rainfall
  for the year
• double aveRain // average monthly
  rainfall
• year in.readString()
• rainfall new double12
• totRain 0
• for ( int i0 iltrainfall.length i )
  
• rainfalli in.readDouble()
• totRain totRain rainfalli
• aveRain totRain / rainfall.length
• writeHeader(year,aveRain)
• for ( int i0 iltrainfall.length i )
  
• if ( rainfalli gt aveRain )
• writeDetail(i,year,rainfalli)

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Processing Variable-sized Arrays

• Example standard deviation of student marks
• data file
• Array of Student objects
• Array size not known
• choose arbitrary size (constant)
• keep count
• Array organization
• not all elements used
• Std Dev formula

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Data File
COSC 1P02 Term Test 111111 Ima First 100 222222 Ma
ry Marvelous 90 333333 Pretty Good 80 444444 Im
Ok 70 555555 Joe Average 60
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Output
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Memory Model
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• Reading data
• traversal
• Student constructor
• termination
• no more data
• no more space
• error
• Computing standard deviation
• array as parameter
• second traversal
• Traversal pattern

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Traversal Pattern
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Std. Dev

• private void genReport ( )
• String course // course name
• String work // name of piece of
  work
• Student students // the class of
  students
• Student aStudent // one student
• int numStd // number of
  students
• double sum // sum of marks
• double ave // average mark
• double std // standard
  deviation
• course stData.readString()
• work stData.readString()
• setUpReport(course,work)
• students new StudentMAX_STD
• numStd 0
• sum 0
• while ( true )
• aStudent new Student(stData)

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Calculating Std. Dev

• private double computeStd ( Student students,
  int numStd, double ave )
• double sum // sum of squares of
  deviations
• double aMark // a student mark
• sum 0
• for ( int i0 iltnumStd i )
• aMark studentsi.getMark()
• sum sum pow(aMark-ave,2)
• return sqrt(sum/numStd)
• // computeStd

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Multidimensional Arrays

• e.g. tables
• 2 or more dimensions
• enrollment data by university and department
• declaration
• type ident or type ident
• creation
• new typeexpr
• subscripting
• identexpr
• length
• regular vs irregular arrays
• variable-sized
• fill upper left corner
• one counter for each dimension

This form is more consistent with other type
declarations. Hence type ident.
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Processing 2-Dimensional Arrays

• random access
• look-up table
• sequential access
• row-major order
• lexicographic order
• pattern
• column-major order
• pattern
• regular arrays

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E.g. Tabulating Enrolments

• data
• right-sized array
• totals
• readStats
• row-major processing
• sumRows
• row processing
• sumCols
• column processing
• sumAll
• row-major processing
• writeStats
• row-major report generation

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Arrays vs Sounds
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Reversing a char array
O L I V E R
R L I V E O
R E I V L O
R E V I L O
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Palindrome Revisited
private void checkPalindromes ( ) int
button String str // string to be checked as
palindrome String reversed // reversed version
of str while ( true ) button
form.accept() if ( button1 ) break str
form.readString("in") reversed
reverse(str) if ( str.equalsIgnoreCase(reversed
) ) form.writeString("out","This is a
palindrome") else form.writeString("ou
t","This is not a palindrome") //
checkPalindromes
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Palindrome Revisited.
private String reverse ( String str ) char
theString // string as array of
characters char c int i theString
str.toCharArray() for ( i0
ilttheString.length/2 i ) c
theStringi theStringi theStringtheString
.length-1-i theStringtheString.length-1-i
c return new String(theString) //
reverse
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Universities
Departments
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Enrollments
public class UStats private final String
UNIVS " Adams"," Beacon"," Madison","
Lexington" private final String DEPTS
"Math.","Business","Comp. Sci.","Biology","French
" private ASCIIDataFile dataFile // file
for input private ASCIIReportFile report //
file for report private ASCIIDisplayer msg //
displayer for messages public UStats ( )
dataFile new ASCIIDataFile() report new
ASCIIReportFile() msg new ASCIIDisplayer()
display() dataFile.close() report.close()
msg.close() // constructor private
void display ( ) int enrol //
enrolment stats int uTotals // University
totals int dTotals // Department
totals int total // grand total msg.writ
eLabel("Processing.....") enrol new
intDEPTS.lengthUNIVS.length readStats(enrol
) uTotals sumRows(enrol) dTotals
sumCols(enrol) total sumAll(enrol) writeSt
ats(enrol,uTotals,dTotals,total) msg.writeLabel
(".....complete") msg.writeEOL() //
display
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Enrollments.
private void readStats ( int stats )
int i, j for ( i0 iltstats.length
i ) for ( j0 jltstatsi.length j )
statsij dataFile.readInt()
// readStats / This method sums the
enrollments by row./ private int sumRows (
int stats ) int sums int i,
j sums new intstats.length for ( i0
iltstats.length i ) sumsi 0 for (
j0 jltstatsi.length j ) sumsi
sumsi statsij return
sums // sumRows
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Enrollments..
//This method sums the enrollments by
column. private int sumCols ( int stats
) int sums int i, j sums new
intstats0.length for ( j0
jltstats0.length j ) sumsj
0 for ( i0 iltstats.length i )
sumsj sumsj statsij
return sums // sumCols //This method
computes the grand sum of the enrollment
statistics. private int sumAll ( int
stats ) int sum int i, j sum
0 for ( i0 iltstats.length i ) for
( j0 jltstatsi.length j ) sum sum
statsij return sum //
sumAll
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Enrollments...
//This method computes the grand sum of the
enrollment statistics. private int sumAll (
int stats ) int sum int i, j sum
0 for ( i0 iltstats.length i )
for ( j0 jltstatsi.length j )
sum sum statsij return
sum // sumAll Alternate Form of
sumAll private int sumAll ( int stats )
int sum int i, j sum 0 for ( int
u stats ) for ( int d u ) sum
sum d return sum // sumAll
Can be read as For each array slice u in stats,
and For each element d in u.
Important to realise that each time the loop
starts u and d represent the next value.
There are no indices, thus they do not need to be
updated. No i or j
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Enrollments.
/ This method initializes the enrolment
report. /
private void initReport ( )
report.setTitle("Enrolment Report",getDateInstance
().format(new Date()))
report.addField("dept","",10) for ( int
i0 iltUNIVS.length i )
report.addField("u"i,UNIVSi,getIntegerInstance(
),10) report.addField("total",
" Total",getIntegerInstance(),10)
// initReport
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Enrollments..
/This method displays the enrollment stats in a
tabular format with labels and totals for each
row and column and a grand total. / private
void writeStats( int stats, int rSums, int
cSums, int sum ) int i, j for ( i0
iltstats.length i ) report.writeString(DEP
TSi) for ( j0 jltstatsi.length j )
report.writeInt(statsij) repor
t.writeInt(rSumsi) report.writeString("T
otal") for ( j0 jltcSums.length j )
report.writeInt(cSumsj) report.writ
eInt(sum,10) // writeStats
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What is a Palindrome?

• A string which reads the same forward and
  reverse.
• E.g.
• This is not a palindrome
• Happy like a fox
• These are all palindromes
• No devil lived on
• I did did I
• Plum was I ere I saw mulp
• Sleep on no peels
• Zeus sees Suez

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Array Declarations
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Good Luck on your Exam!!